1. Field of the Invention
This invention relates to an image reading apparatus, and particularly to an image reading apparatus using image pickup means (reading means) comprising a plurality of light receiving elements such as CCDs arranged in a one-dimensional direction to highly accurately read the image information of an original such as film or OHP while achieving the efficiency of utilization of illuminating light.
2. Related Background Art
As image reading apparatuses using reading means such as a CCD to read an original such as film or OHP, there are widely known constructions as shown in FIGS. 1 and 2 of the accompanying drawings.
FIG. 1 is a schematic view of the essential portions of a reflection type image reading apparatus according to the prior art. In a reading head 103, there are disposed two light sources 104A and 104B, two reflectors 105A and 105B corresponding to the light sources 104A and 104B, an imaging optical system 106 and a line sensor 107. An original 101, shown placed on an original supportion glass table 102, illuminated with beams of light from the light sources 104A and 104B is imaged on the line sensor 107 by the imaging optical system 106. In FIG. 1, a reading head 103 is scanned in the direction of arrow A to thereby effect the reading of the reflection type original.
FIG. 2 is a schematic view of the essential portions of a transmission type image reading apparatus according to the prior art. In FIG. 2, a beam of light from a light source 104c and a beam of light emitted from the light source 104c toward a reflecting mirror 105c and reflected by the reflecting mirror 105c are condensed by a condenser lens 108 to thereby illuminate a transmission type original 109. The original 109 is imaged on a line sensor 107 by an imaging optical system 106. The light source 104c and the pupil of the imaging optical system 106 are adapted to be in conjugate relationship with each other. In FIG. 2, the line sensor 107 is scanned in the direction of arrow B to thereby perform the reading of the transmission type original.
Light source means used in the prior-art image reading apparatuses merely emits a beam of light and the light source itself has no optical condensing action. Therefore, the quantity of illuminating light onto the surface of an original is liable to be deficient, and this has led to the problem that the reading speed of the image reading apparatus is limited.
As methods of solving these problems, there are the following methods.
(1) A method of driving the light source with a high voltage to increase the luminance of the light source itself. This method, however, gives rise to the problem that a tube forming the light source becomes bulky to thereby make the entire apparatus bulky and the amount of generated heat beams great causing the apparatus to become hot. PA1 (2) A method of mounting near the light source a reflector for reflecting that part of the beam of light emitted from the light source which is emitted toward the side opposite to the original toward the original side. This method, however, gives rise to the problem that the entire apparatus becomes bulky and necessitates an increase in the number of parts that complicates the entire apparatus. PA1 (1-1) that when the image information of a transmission type original illuminated with a beam of light from the light source means is to be imaged, by imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a fluorescent lamp and the fluorescent lamp causes a part of a beam of light from the fluorescent lamp to be condensed on the surface of the original by the optical action of the tube surface thereof. PA1 (1-1-1) that the tube surface of the fluorescent lamp comprises at least one reflecting surface or/and transmitting surface differing in refractive power in the main scanning section and in the sub scanning section, and PA1 (1-1-2) that the tube surface comprises a cylindrical surface, a toric surface or a Fresnel surface. PA1 (1-2) that when the image information of a transmission type original illuminated with a beam of light from the light source means is to be imaged, by imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a fluorescent lamp and the fluorescent lamp condenses a beam of light therefrom by the optical action of the tube surface thereof so as to become a linear beam of light on the surface of the original in the main scanning section. PA1 (1-2-1) that the fluorescent lamp condenses the beam of light therefrom in the sub scanning section toward the entrance pupil surface of the imaging means by the optical action of the tube surface thereof, PA1 (1-2-2) that the tube surface of the fluorescent lamp comprises at least one reflecting surface or/and transmitting surface differing in refractive power in the main scanning section and in the sub scanning section, and PA1 (1-2-3) that the tube surface comprises a cylindrical surface, a toric surface or a Fresnel surface. PA1 (1-3) that the light source means is a fluorescent lamp and at least some of a beam of light reflected on and/or transmitted through the tube surface of the fluorescent lamp is condensed on the surface of the original by the reflecting action and or the transmitting action. PA1 (1-3-1) that said at least some of the beam of light is condensed on the surface of the original in the arrangement section of the plurality of light receiving elements of the reading means, and PA1 (1-3-2) that said at least some of the beam of light is condensed on the entrance pupil surface of the imaging means in a plane perpendicular to the arrangement section of the plurality of light receiving elements. PA1 (2-1) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged on the surface of the reading means by imaging means and the image information of the original is to be read, the light source means has a cathode tube and the tube surface of the cathode tube which is opposed to the surface of the original comprises a flat surface relative to the surface of the original. PA1 (2-2) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged on the surface of the reading means by imaging means and the image information of the original is to be read, the light source means has a cathode tube having a fluorescent surface and the fluorescent surface of the cathode tube comprises a flat surface relative to the surface of the original. PA1 (2-3) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged on the surface of the reading means by imaging means and the image information of the original is to be read, the light source means has a cathode tube having a fluorescent surface and that tube surface of the cathode tube which is opposed to the surface of the original comprises a flat surface relative to the surface of the original or/and the fluorescent surface of the cathode tube comprises a flat surface relative to the surface of the original. PA1 (3-1) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged, by the imaging means, on the surface of reading means in which a plurality of picture elements (pixels) are one-dimensionally arranged in a main scanning direction, and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the cross-sectional shape of that surface of the light source means which emits the beam of light and is adjacent to the surface of the original comprises a flat surface relative to the main scanning direction and comprises a concave surface relative to the sub scanning direction. PA1 (3-2) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged, by the imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction, and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a fluorescent lamp and the cross-sectional shape of that tube surface of the fluorescent lamp which emits the beam of light and is adjacent to the surface of the original comprises a flat surface relative to the main scanning direction and comprises a concave surface relative to the sub scanning direction, and a fluorescent material is applied to the inner side of the tube surface. PA1 (3-3) that when the image information of an original illuminated with a beam of light from the light source means is to be imaged, by the imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction, and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a fluorescent lamp and the cross-sectional shape of that tube surface of the fluorescent lamp which emits the beam of light and faces the surface of the original comprises a flat surface relative to the main scanning direction and comprises a concave surface relative to the sub scanning direction, and in the fluorescent lamp a fluorescent material is applied to an inner surface of the tube surface and an inner surface of the tube surface opposite to the tube surface located at the surface side of the original. PA1 (3-4) that when image information of an original illuminated with a beam of light from the light source means is to be imaged, by the imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction, and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a diffusing plate formed so as to cover the range of a one-dimensional reading area on the surface of the original in the main scanning direction, and a light source unit in which a plurality of incandescent lamps are arranged in each of the main scanning direction and the sub scanning direction, and the cross-sectional shape of the diffusing surface of the diffusing plate which faces the surface of the original comprises a flat surface relative to the main scanning direction and comprises a concave surface relative to the sub scanning direction, and the plurality of incandescent lamps are arranged in each of the main scanning direction and the sub scanning direction along the outer side surface of the diffusing plate. PA1 (3-5) that when image information of an original illuminated with a beam of light from the light source means is to be imaged, by the imaging means, on the surface of reading means in which a plurality of picture elements are one-dimensionally arranged in a main scanning direction, and the original and the reading means are to be moved relative to each other in a sub scanning direction substantially orthogonal to the main scanning direction to thereby read the original, the light source means has a light source unit in which a plurality of light emitting diodes are arranged in each of the main scanning direction and the sub scanning direction so as to cover the range of a one-dimensional reading area on the surface of the original in the main scanning direction, and the state of arrangement of the plurality of light emitting diodes constituting the light source unit is flat configuration relative to the main scanning direction and is concave configuration relative to the sub scanning direction.
Further, there arises the problem that in order to effect efficient illumination, adjusting means for setting the relative positional relation between the light source and the reflector to predetermined accuracy is required.